In one aspect, the present invention provides for a compound of Formula I in which in Formula I, the variables X1, X2a, X2b, X2c, R1, B, L, E, A and the subscript n are as defined herein. In another aspect, the present invention provides for pharmaceutical compositions comprising compounds of Formula I as well as methods for using compounds of Formula I for the treatment of diseases and conditions (e.g., cancer, thrombocythemia, etc) characterized by the expression or over-expression of Bcl-2 anti-apoptotic proteins, e.g., of anti-apoptotic Bcl-xL proteins.